It is known that a non-electroconductive material, such as plastics, may be rendered electroconductive by the addition of an electrically conductive powder. Examples of known electroconductive powders include metal powders, carbon black, and tin oxide doped with antimony or a like dopant. Addition of metal powder or carbon black to plastics makes the plastics black, which can limit the utility of the plastics. Addition of tin oxide doped with antimony, etc. makes plastics bluish black, which can also limit the utility of the plastics as with the case of adding carbon black. In addition, using antimony involves the problem of environmental burdens. Hence, various studies have been reported on tin oxide free from an environmentally unsound dopant, such as antimony.
Patent literatures 1 and 2 (see below) propose tin oxide doped with fluorine that is an element with low environmental burden. Specifically, patent literature 1 teaches that tin oxide powder is brought into contact with 10 to 40 vol % fluorine gas in an inert gas atmosphere to provide fluorine-doped tin oxide exhibiting electroconductivity. Patent literature 2 discloses transparent tin oxide powder containing 0.3% to 5.0% of fluorine and free from any of antimony, phosphorus, and indium. The transparent tin oxide powder is obtained by adding fluorine or a fluorine compound to an aqueous solution of tin hydroxide, dehydrating the mixture, and heating the resulting solid in an inert atmosphere with a humidity of 50% or higher at 350° to 800° C.